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What are Cartograms?

Cartograms are maps in which the areas of regions (e.g. states, provinces) are rescaled to be proportional to statistical data (e.g. population size, gross domestic product). Cartograms are called “contiguous” if they maintain the topology of the conventional map (ie. regions are displayed as neighbours on the cartogram if and only If they are geographic neighbours) [1].

Creating such cartograms has traditionally been a complex endeavour, one that usually only academics and experts attempt and explore. However, producing contiguous cartograms should not be the privilege of only a handful of experts in cartography. Journalists or bloggers, for example, may also benefit from a cartogram as an intriguing illustration of their own data. Similarly, high school students may enrich a term paper with a cartogram that can summarize data more e ectively than raw numeric tables.

Why go-cart.io?

Until now, the creation of contiguous cartograms has been far from user-friendly, requiring computer skills that even experts in data visualization typically do not possess. In the past, publications that introduced new cartogram algorithms rarely included computer code. Some authors of more recent publications have posted their code online [1,2], but their software usually requires technical knowledge (e.g. about shell scripting, compiling, GIS) that pose insurmountable obstacles for most users. This is where go-cart.io comes in. With an interface that is easy for even non-experts to use, go-cart.io eliminates hurdles and provides a convenient way to create readable cartograms.

How Does go-cart.io Work?

While previous cartogram generators required users to install software (e.g. Java) on their computer, go-cart.io is based on JavaScript that can be run in any contemporary web browser without additional downloads. We decided to simplify the data input as much as possible. We have curated a “library” of topologies so that users do not need GIS expertise to create geospatial vector data. After data are transmitted, a remote server calculates the cartogram transformation with the recently developed fast flow-based algorithm [1]. Because the calculation is entirely server- side, we eliminate any dependence on the client’s hardware. For typical input, the calculation finishes within 10 to 15 seconds. If the calculation needs substantially longer, the application displays a bar chart instead of a cartogram as a fallback. The cartogram is displayed in the browser window side by side with the conventional (i.e. equal-area) map. The user can explore both maps with various interactive features implemented using the D3.js library [3].

What is the Fast Flow-based Algorithm?

Until now, the creation of contiguous cartograms has been far from user-friendly, requiring computer skills that even experts in data visualization typically do not possess. In the past, publications that introduced new cartogram algorithms rarely included computer code. Some authors of more recent publications have posted their code online [1,2], but their software usually requires technical knowledge (e.g. about shell scripting, compiling, GIS) that pose insurmountable obstacles for most users. This is where go-cart.io comes in. With an interface that is easy for even non-experts to use, go-cart.io eliminates hurdles and provides a convenient way to create readable cartograms.

References

  1. Gastner MT, Seguy V, More P. Fast flow-based algorithm for creating density-equalizing map projections. ProcNatl Acad Sci USA 115(10):E2156–E2164 (2018).
  2. Sun S. A fast, free-form rubber-sheet algorithm for contiguous area cartograms. Int J Geogr Inf Sci 27(3):567–593(2013).
  3. Bostock M, Ogievetsky V, Heer J. D3 Data-Driven Documents. IEEE Trans Vis Comput Graph 17(12):2301–2309(2011).